Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

Included in:
AbstractAdapter
Defined in:
lib/active_record/connection_adapters/abstract/database_statements.rb

Defined Under Namespace

Classes: PartialQueryCollector

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#transaction_manager ⇒ Object (readonly)

:nodoc:



273
274
275
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 273

def transaction_manager
  @transaction_manager
end

Instance Method Details

#add_transaction_record(record) ⇒ Object

Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.



287
288
289
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 287

def add_transaction_record(record)
  current_transaction.add_record(record)
end

#begin_db_transaction ⇒ Object

Begins the transaction (and turns off auto-committing).



296
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 296

def begin_db_transaction()    end

#begin_isolated_db_transaction(isolation) ⇒ Object

Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.

Raises:



310
311
312
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 310

def begin_isolated_db_transaction(isolation)
  raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end

#cacheable_query(klass, arel) ⇒ Object

This is used in the StatementCache object. It returns an object that can be used to query the database repeatedly.



46
47
48
49
50
51
52
53
54
55
56
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 46

def cacheable_query(klass, arel) # :nodoc:
  if prepared_statements
    sql, binds = visitor.accept(arel.ast, collector).value
    query = klass.query(sql)
  else
    collector = PartialQueryCollector.new
    parts, binds = visitor.accept(arel.ast, collector).value
    query = klass.partial_query(parts)
  end
  [query, binds]
end

#commit_db_transaction ⇒ Object

Commits the transaction (and turns on auto-committing).



315
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 315

def commit_db_transaction()   end

#default_sequence_name(table, column) ⇒ Object 



329
330
331
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 329

def default_sequence_name(table, column)
  nil
end

#delete(arel, name = nil, binds = []) ⇒ Object

Executes the delete statement and returns the number of rows affected.



174
175
176
177
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 174

def delete(arel, name = nil, binds = [])
  sql, binds = to_sql_and_binds(arel, binds)
  exec_delete(sql, name, binds)
end

#empty_insert_statement_value ⇒ Object 



401
402
403
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 401

def empty_insert_statement_value
  "DEFAULT VALUES"
end

#exec_delete(sql, name = nil, binds = []) ⇒ Object

Executes delete sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.



136
137
138
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 136

def exec_delete(sql, name = nil, binds = [])
  exec_query(sql, name, binds)
end

#exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil) ⇒ Object

Executes insert sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.



128
129
130
131
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 128

def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)
  sql, binds = sql_for_insert(sql, pk, nil, sequence_name, binds)
  exec_query(sql, name, binds)
end

#exec_query(sql, name = "SQL", binds = [], prepare: false) ⇒ Object

Executes sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

Raises:

  • (NotImplementedError) 


121
122
123
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 121

def exec_query(sql, name = "SQL", binds = [], prepare: false)
  raise NotImplementedError
end

#exec_rollback_db_transaction ⇒ Object

:nodoc:



323
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 323

def exec_rollback_db_transaction() end

#exec_update(sql, name = nil, binds = []) ⇒ Object

Executes update sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.



148
149
150
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 148

def exec_update(sql, name = nil, binds = [])
  exec_query(sql, name, binds)
end

#execute(sql, name = nil) ⇒ Object

Executes the SQL statement in the context of this connection and returns the raw result from the connection adapter. Note: depending on your database connector, the result returned by this method may be manually memory managed. Consider using the exec_query wrapper instead.

Raises:

  • (NotImplementedError) 


114
115
116
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 114

def execute(sql, name = nil)
  raise NotImplementedError
end

#initialize ⇒ Object 



6
7
8
9
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 6

def initialize
  super
  reset_transaction
end

#insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) ⇒ Object Also known as: create

Executes an INSERT query and returns the new record’s ID

id_value will be returned unless the value is nil, in which case the database will attempt to calculate the last inserted id and return that value.

If the next id was calculated in advance (as in Oracle), it should be passed in as id_value.



160
161
162
163
164
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 160

def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
  sql, binds = to_sql_and_binds(arel, binds)
  value = exec_insert(sql, name, binds, pk, sequence_name)
  id_value || last_inserted_id(value)
end

#insert_fixture(fixture, table_name) ⇒ Object

Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle). Most of adapters should implement ‘insert_fixtures` that leverages bulk SQL insert. We keep this method to provide fallback for databases like sqlite that do not support bulk inserts.



343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 343

def insert_fixture(fixture, table_name)
  fixture = fixture.stringify_keys

  columns = schema_cache.columns_hash(table_name)
  binds = fixture.map do |name, value|
    if column = columns[name]
      type = lookup_cast_type_from_column(column)
      Relation::QueryAttribute.new(name, value, type)
    else
      raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.)
    end
  end

  table = Arel::Table.new(table_name)

  values = binds.map do |bind|
    value = with_yaml_fallback(bind.value_for_database)
    [table[bind.name], value]
  end

  manager = Arel::InsertManager.new
  manager.into(table)
  manager.insert(values)
  execute manager.to_sql, "Fixture Insert"
end

#insert_fixtures(fixtures, table_name) ⇒ Object

Inserts a set of fixtures into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).



371
372
373
374
375
376
377
378
379
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 371

def insert_fixtures(fixtures, table_name)
  ActiveSupport::Deprecation.warn(<<-MSG.squish)
    `insert_fixtures` is deprecated and will be removed in the next version of Rails.
    Consider using `insert_fixtures_set` for performance improvement.
  MSG
  return if fixtures.empty?

  execute(build_fixture_sql(fixtures, table_name), "Fixtures Insert")
end

#insert_fixtures_set(fixture_set, tables_to_delete = []) ⇒ Object 



381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 381

def insert_fixtures_set(fixture_set, tables_to_delete = [])
  fixture_inserts = fixture_set.map do |table_name, fixtures|
    next if fixtures.empty?

    build_fixture_sql(fixtures, table_name)
  end.compact

  table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name table}".dup }
  total_sql = Array.wrap(combine_multi_statements(table_deletes + fixture_inserts))

  disable_referential_integrity do
    transaction(requires_new: true) do
      total_sql.each do |sql|
        execute sql, "Fixtures Load"
        yield if block_given?
      end
    end
  end
end

#join_to_update(update, select, key) ⇒ Object Also known as: join_to_delete

The default strategy for an UPDATE with joins is to use a subquery. This doesn’t work on MySQL (even when aliasing the tables), but MySQL allows using JOIN directly in an UPDATE statement, so in the MySQL adapters we redefine this to do that.



422
423
424
425
426
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 422

def join_to_update(update, select, key) # :nodoc:
  subselect = subquery_for(key, select)

  update.where key.in(subselect)
end

#query(sql, name = nil) ⇒ Object

:nodoc:



105
106
107
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 105

def query(sql, name = nil) # :nodoc:
  exec_query(sql, name).rows
end

#query_value(sql, name = nil) ⇒ Object

:nodoc:



97
98
99
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 97

def query_value(sql, name = nil) # :nodoc:
  single_value_from_rows(query(sql, name))
end

#query_values(sql, name = nil) ⇒ Object

:nodoc:



101
102
103
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 101

def query_values(sql, name = nil) # :nodoc:
  query(sql, name).map(&:first)
end

#reset_sequence!(table, column, sequence = nil) ⇒ Object

Set the sequence to the max value of the table’s column.



334
335
336
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 334

def reset_sequence!(table, column, sequence = nil)
  # Do nothing by default. Implement for PostgreSQL, Oracle, ...
end

#reset_transaction ⇒ Object

:nodoc:



281
282
283
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 281

def reset_transaction #:nodoc:
  @transaction_manager = ConnectionAdapters::TransactionManager.new(self)
end

#rollback_db_transaction ⇒ Object

Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.



319
320
321
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 319

def rollback_db_transaction
  exec_rollback_db_transaction
end

#rollback_to_savepoint(name = nil) ⇒ Object 



325
326
327
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 325

def rollback_to_savepoint(name = nil)
  exec_rollback_to_savepoint(name)
end

#sanitize_limit(limit) ⇒ Object

Sanitizes the given LIMIT parameter in order to prevent SQL injection.

The limit may be anything that can evaluate to a string via #to_s. It should look like an integer, or an Arel SQL literal.

Returns Integer and Arel::Nodes::SqlLiteral limits as is.



411
412
413
414
415
416
417
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 411

def sanitize_limit(limit)
  if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
    limit
  else
    Integer(limit)
  end
end

#select_all(arel, name = nil, binds = [], preparable: nil) ⇒ Object

Returns an ActiveRecord::Result instance.



59
60
61
62
63
64
65
66
67
68
69
70
71
72
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 59

def select_all(arel, name = nil, binds = [], preparable: nil)
  arel = arel_from_relation(arel)
  sql, binds = to_sql_and_binds(arel, binds)

  if preparable.nil?
    preparable = prepared_statements ? visitor.preparable : false
  end

  if prepared_statements && preparable
    select_prepared(sql, name, binds)
  else
    select(sql, name, binds)
  end
end

#select_one(arel, name = nil, binds = []) ⇒ Object

Returns a record hash with the column names as keys and column values as values.



76
77
78
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 76

def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end

#select_rows(arel, name = nil, binds = []) ⇒ Object

Returns an array of arrays containing the field values. Order is the same as that returned by columns.



93
94
95
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 93

def select_rows(arel, name = nil, binds = [])
  select_all(arel, name, binds).rows
end

#select_value(arel, name = nil, binds = []) ⇒ Object

Returns a single value from a record



81
82
83
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 81

def select_value(arel, name = nil, binds = [])
  single_value_from_rows(select_rows(arel, name, binds))
end

#select_values(arel, name = nil, binds = []) ⇒ Object

Returns an array of the values of the first column in a select:

select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]



87
88
89
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 87

def select_values(arel, name = nil, binds = [])
  select_rows(arel, name, binds).map(&:first)
end

#supports_statement_cache? ⇒ Boolean

Returns true when the connection adapter supports prepared statement caching, otherwise returns false

Returns:

  • (Boolean) 


181
182
183
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 181

def supports_statement_cache? # :nodoc:
  true
end

#to_sql(arel_or_sql_string, binds = []) ⇒ Object

Converts an arel AST to SQL



12
13
14
15
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 12

def to_sql(arel_or_sql_string, binds = [])
  sql, _ = to_sql_and_binds(arel_or_sql_string, binds)
  sql
end

#transaction(requires_new: nil, isolation: nil, joinable: true) ⇒ Object

Runs the given block in a database transaction, and returns the result of the block.

Nested transactions support

Most databases don’t support true nested transactions. At the time of writing, the only database that supports true nested transactions that we’re aware of, is MS-SQL.

In order to get around this problem, #transaction will emulate the effect of nested transactions, by using savepoints: dev.mysql.com/doc/refman/5.7/en/savepoint.html Savepoints are supported by MySQL and PostgreSQL. SQLite3 version >= ‘3.6.8’ supports savepoints.

It is safe to call this method if a database transaction is already open, i.e. if #transaction is called within another #transaction block. In case of a nested call, #transaction will behave as follows:

  • The block will be run without doing anything. All database statements that happen within the block are effectively appended to the already open database transaction.

  • However, if :requires_new is set, the block will be wrapped in a database savepoint acting as a sub-transaction.

Caveats

MySQL doesn’t support DDL transactions. If you perform a DDL operation, then any created savepoints will be automatically released. For example, if you’ve created a savepoint, then you execute a CREATE TABLE statement, then the savepoint that was created will be automatically released.

This means that, on MySQL, you shouldn’t execute DDL operations inside a #transaction call that you know might create a savepoint. Otherwise, #transaction will raise exceptions when it tries to release the already-automatically-released savepoints:

Model.connection.transaction do  # BEGIN
  Model.connection.transaction(requires_new: true) do  # CREATE SAVEPOINT active_record_1
    Model.connection.create_table(...)
    # active_record_1 now automatically released
  end  # RELEASE SAVEPOINT active_record_1  <--- BOOM! database error!
end

Transaction isolation

If your database supports setting the isolation level for a transaction, you can set it like so:

Post.transaction(isolation: :serializable) do
  # ...
end

Valid isolation levels are:

  • :read_uncommitted

  • :read_committed

  • :repeatable_read

  • :serializable

You should consult the documentation for your database to understand the semantics of these different levels:

An ActiveRecord::TransactionIsolationError will be raised if:

  • The adapter does not support setting the isolation level

  • You are joining an existing open transaction

  • You are creating a nested (savepoint) transaction

The mysql2 and postgresql adapters support setting the transaction isolation level.



260
261
262
263
264
265
266
267
268
269
270
271
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 260

def transaction(requires_new: nil, isolation: nil, joinable: true)
  if !requires_new && current_transaction.joinable?
    if isolation
      raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction"
    end
    yield
  else
    transaction_manager.within_new_transaction(isolation: isolation, joinable: joinable) { yield }
  end
rescue ActiveRecord::Rollback
  # rollbacks are silently swallowed
end

#transaction_isolation_levels ⇒ Object 



298
299
300
301
302
303
304
305
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 298

def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end

#transaction_open? ⇒ Boolean

Returns:

  • (Boolean) 


277
278
279
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 277

def transaction_open?
  current_transaction.open?
end

#transaction_state ⇒ Object 



291
292
293
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 291

def transaction_state
  current_transaction.state
end

#truncate(table_name, name = nil) ⇒ Object

Executes the truncate statement.

Raises:

  • (NotImplementedError) 


141
142
143
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 141

def truncate(table_name, name = nil)
  raise NotImplementedError
end

#update(arel, name = nil, binds = []) ⇒ Object

Executes the update statement and returns the number of rows affected.



168
169
170
171
 
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 168

def update(arel, name = nil, binds = [])
  sql, binds = to_sql_and_binds(arel, binds)
  exec_update(sql, name, binds)
end